1. Field of the Invention
The present invention relates to a data compression apparatus for compressing data such as image data, and a data compression program storage medium storing a data compression program, which causes an information processing apparatus such as a computer to operate as the data compression apparatus.
2. Description of the Related Art
Hitherto, in order to reduce storage capacity or traffic, there is widely adopted a technology of compressing data such as image data.
For example, Japanese Patent Laid Open Gazette TokuKai Hei.5-328142 discloses a technology as set forth below.
As to image data, data size is reduced in such a manner that an attribute plane of individual color, in which print set up information is recorded, is subjected to a reversible compression, and a plane of individual color of CMYK is non-reversible compression.
Japanese Patent Publication TokuKai No. 2002-236566 discloses a technology in which image data is compressed for each color plane, and individual color planes of the compressed image data are transferred to a printer every the block in order according to the size or the compressibility, so that the printer expands the transferred image data and forms a color image in accordance with the expanded image data.
Here, there will be explained a system to which a data compression technology is applied.
FIG. 1 is a view useful for understanding an example of a print system to which a data compression technology is applied. FIG. 2 is a view useful for understanding a data processing in the print system.
As shown in FIG. 1, the print system comprises a host controller 100, an interface equipment 200, and a printer 300. The host controller 100 is connected to the interface equipment 200 via an all-purpose interface cable 150 such as SCSI. And the interface equipment 200 is connected to the printer 300 via a dedicated interface cable 250.
In the host controller 100, as shown in FIG. 2, data 11 of images and characters described in various languages and formats, such as PDF, PS, TIFF, are divided into image (CT; Continuous Tone) data and characters and lines (LW; Line Work) data, and RIP (Raster Image Processing) is applied to such two types of data, so that bit map data 12A and 13A are created. Further, data compression processing is applied to such two types of data, so that non-reversible compression data 14 is created on the CT and reversible compression data 15 is created on the LW. Those types of compression data 14 and 15 are transmitted from the host controller 100 via the all-purpose interface cable 150 shown in FIG. 1 to the interface equipment 200. The interface equipment 200 applies a data expansion processing to the transmitted compression data 14 and 15 to creates bit map data 12B and 13B associated with the bit map data 12A and 13A, respectively, which are in the state before an application of the data compression processing by the host controller 100. With respect to the CT data, when the host controller 100 performs the data compression, the non-reversible compression processing is carried out. Accordingly, it is difficult to completely return the CI data after the data expansion, or the bit map data 12B to the CI data before the data compression, or the bit map data 12A. However, it is possible to reproduce the substantially same bit map data. With respect to the LW data, when the host controller 100 performs the data compression, the reversible compression processing is carried out. Accordingly, it is possible to restore the LW data after the data expansion, or the bit map data 13B to the LW data before the data compression, or the bit map data 13A.
The interface equipment 200 synthesizes the CI data after the data expansion or the bit map data 12B with the LW data after the data expansion or the bit map data 13B, and transmits the synthesized data to the printer 300 together with halftone dot information and the like in form of a tag. The printer 300 prints out an image in accordance with the bit map data received from the interface equipment 200 and the attached tag information.
In the event that there is a need that the host controller 100 and the interface equipment 200 are individually constructed in form of a separated apparatus, for example, in a case where the host controller 100 and the interface equipment 200 are mutually isolated, and in case of a system in which the interface equipment 200 receives image data from a plurality of host controllers, as shown in FIG. 2, there is provided such an arrangement that data is transferred to the interface equipment 200 through data compression by the host controller 100, so that the interface equipment 200 performs data expansion. This arrangement makes it possible to reduce a transfer time of the data from the host controller 100 to the interface equipment 200, and thereby improving the productivity of the print.
Generally, with respect to the CT data, there is adopted a compression system such as JPEG, which is high in compressibility, while it is non-reversible. On the other hand, with respect to the LW data, there is adopted a reversible compression system such as PackBits.
However, the compression system such as JPEG takes a lot of time for compression processing in software, and is a cause of the deterioration of the processing ability of the compression processing system in its entirety. Further, according to the compression system such as JPEG, the image quality might decrease when the compressibility is raised. When the compression processing is applied to the CT data representative of the image of the color, those problems become especially remarkable.